1. Field of the Invention
The present invention relates to an electrodeless lighting system using microwave, and particularly, to an apparatus for blocking ambient air of an electrodeless lighting system for preventing ambient air from flowing into an area where a bulb and a mesh screen are installed.
2. Description of the Background Art
Generally, an electrodeless lighting system is an apparatus for emitting visible rays or ultraviolet rays by radiating microwave to an electrodeless plasma bulb, and it has longer life span that that of incandescent lamp or fluorescent lamp and has superior lighting effect.
FIG. 1 is a longitudinal cross-sectional view showing an electrodeless lighting system according to the conventional art.
The conventional electrodeless lighting system comprises: a magnetron 2 installed in a case 1 for generating microwave; a high voltage generator 3 for providing the magnetron 2 with high voltage after raising the utility AC power source to the high voltage; a waveguide 4 for transmitting the microwave generated in the magnetron 2; a mesh screen 6 installed on an outlet portion of the waveguide for blocking a leakage of the microwave and for passing light; and a bulb 5, in which filled material becomes plasma by the microwave transmitted through the waveguide 4 to emit the light, located in the mesh screen 6.
In the electrodeless lighting system like above, a reflector 7 for reflecting forward the light generated in the bulb 5 is disposed around the mesh screen 6 in front of the case 1, and a mirror 8 for passing the microwave transmitted through the waveguide 4 and reflecting the light radiated from the bulb 5 is installed in an outlet portion 4a of the waveguide 4.
On the other hand, a fan housing 9a, a cooling fan 9b, and a fan motor 9c are installed on rear side of the case 1 for cooling down the magnetron 2 and the high voltage generator 3 as air cooling method.
In addition, a bulb motor 5b is installed on bottom surface of the waveguide 4 so as to rotate and cool down the bulb 5, and a bulb shaft 5a which is connected as penetrating the waveguide 4 is installed between the bulb motor 5b and the bulb 5.
And holes 4b and 8a are formed on the waveguide 4 and on the mirror 8 so as to pass the bulb shaft 5a. 
In the electrodeless lighting system constructed above, when an electric source is applied to the high voltage generator 3, the high voltage generator 3 raises the utility AC power to high voltage and provides the magnetron 2 with the high voltage. And the magnetron 2 generates the microwave having ultra high frequency.
The generated microwave is radiated into the mesh screen 6 through the waveguide 4, and discharges the material filled in the bulb 5 to emit the light having its own emission spectrum. In addition, the light generated in the bulb 5 is reflected on the mirror 8 and the reflector 7 toward front side to illuminate a lighting area.
On the other hand, when the electrodeless lighting system is operated, the magnetron 2 and the high voltage generator 3 generate heat of high temperature. Therefore, the fan motor 9c and the cooling fan 9b are operated to cool down inside of the case 1 as the air cooling method.
That is, when the cooling fan 9b is operated, the air which is flowed into the case 1 through the fan housing 9a cools down the magnetron 2 and the high voltage generator 3 and then goes out through a discharge hole 1a. 
However, the ambient air flowed into the case 1 as the cooling fan 9b is operated is also flowed in the light emitting area in which the bulb 5 and the mesh screen 6 are located through the hole 4b formed on a center part of the waveguide 4 and the hole 8a of the mirror 8.
In addition, impurities such as dust are also flowed with the ambient air when the air is flowed into the light emitting area where the bulb 5 and the mesh screen 6 are located, and the flowed ambient air and the impurities oxidizes the mesh screen 6 which is made using a metal. And therefore, the life span of the mesh screen 6 is reduced.
That is, the light emitting area in which the mesh screen 6 is located is considerably high temperature environment because the bulb 5 generates high temperature over 1000° C., and at that time, the ambient air and the impurities flowed into the light emitting area contact to the mesh screen 6 of metal, and therefore, the oxidation rate is greatly increased.
Therefore, if the mesh screen is oxidized and burned, the microwave may leak. Therefore, the stability of the lighting apparatus is decreased, and the maintenance cost of the lighting apparatus is very high because the mesh screen 6 needs to be replaced frequently.